9 MISC. PUBLICATION 363, U. 8S. DEPT. OF AGRICULTURE 
But to carry out a program of soil and wildlife conservation vege- 
tation must be utilized intelligently. Where considerable numbers 
of plants are to be employed, it is essential to know as much as pos- 
sible about. every species of tree, shrub, or herb we propose for 
planting. We should know where and on what soils a species will 
grow, what degree of drought or moisture it can endure, the nature - 
and extent of its root system, its susceptibility to insects and disease, 
its aggressiveness, its relation to other species, its value to the land- 
owner as a crop-producing plant, and its use as food or cover by 
wildlife. 
In other words, the time is opportune to take inventory of the 
stock on hand; not to show how much has been lost, but to determine 
what is left to build with, and how most wisely to employ it. There 
exists a widely distributed mass of information concerning plants, 
which, if assembled and properly classified, may assist materially in 
dealing with soil and wildlife conservation. 
This publication presents an indexed list of woody plants growing 
in the United States, naming each species as unmistakably as possi- 
ble, and giving all available data pertinent to its use in erosion control 
and wildlife conservation. Such an inventory as this shows not only 
what is known about each species of plant but by inference what is 
not known. Every species is potentially a valuable resource in itself. 
The development of each plant resource eventually may disclose a 
crop as yet unsuspected. 
Tt may be noted that this indexed list is not intended for use in the 
identification of plants, although characters listed here may assist in 
making determinations. There are manuals to cover the entire coun- 
try, with the exception of Arizona and Texas. After identification is 
certain, this publication may be consulted for data on the use of any 
given woody plant. 
THE RELATION OF VEGETATION TO SOIL CONSERVATION 
Under our present agricultural system we are concerned with the 
manipulation of cultivated crops in such a manner as to keep the 
maximum of cover on the soil as much of the time as is possible. 
Such manipulated, cultivable crops may be classed as temporary 
vegetation. The permanent class will include plants that are per- 
mitted to remain on the ground without disturbance, except that 
incident to gathering from them such periodic crops as they may pro- 
duce. It is with the permanent class that this publication deals. 
As every soil conservationist knows, there is a very definite relation 
between the density of the plant cover on the soil, the amount of soil 
lost through erosion, and the productivity of that soil. These three 
functions vary in a regular and direct manner, and there is no reason 
to believe that they have not always done so. Soil is formed partly 
by vegetation, and vegetation is in good part a product of the soil. 
Reasoning from our observation of natural conditions, we must expect 
to direct our efforts to control erosion toward revegetation, since it is 
known that erosion starts with the destruction of the plant cover and 
that the kind and density of vegetation is more important in influenc- 
ing putson and erosion than is steepness of slope or intensity of 
rainfall. 
1 Data from the U. S. Forest Service, Intermountain Station, Ogden, Utah. 
